As a general rule, it should be used at maxed precision when doing so will with a high degree of certainty result in killing off enemies faster without the risk of misses, or when there is a risk of misses and enemies' armour is so high that the extra damage justifies both the increased cost and the increased risk.
Two-handed weapons + Guerrilla + Power Stance is a net gain in damage even on a imagined target dummy. 125% damage * 2 = 250% for a increase of 50% AP and 10% reduced hit chance. If you have anyway 100% hit-chance it becomes even better.
one spell... death punch. without even buffing, at level 17 my mage does over 1600 damage with just that one spell. yeesh.
My two fighters need buffs for that. And do it 4-5 times per turn ;-)
Alternatively they do about 16000 damage with whirlwind. And well than there is flurry, which is a waste to use on anything, but bosses. ;-)
